Best to actually weigh it's axle, fully loaded ready to go RV'ing....but....while shopping...ball park guesstimating you will need both listed dry weights & ratings AND the GVWR of the trailer(s)
You can figure the tongue or PIN percentage weight of it's dry condition...then use that percentage to multiply the GVWR and that begets a ball park tongue or PIN to figure what your TV is rated for
Of course you should also weigh your TV axle's fully loaded ready to go in order to not be guesstimating there too